1. Field of the Invention
A semiconductor device has a doped silicon carbide heterojunction.
2. Description of the Related Art
Gallium nitride (GaN) is a typical wide-bandgap semiconductor material that has potential applications in high-speed, high power transistor devices. One of the main drawbacks to the production of these devices is the limited availability of suitable substrates for epitaxial growth. A high-quality bulk single crystal substrate such as silicon carbide (SiC), having low cost and having a large area, is desirable for the growth of GaN and other types of epitaxial layers for device fabrication. In one example of a related art technology, the GaN epitaxial layer is homoepitaxially grown on a single crystal GaN substrate. However, the cost and availability of these wafers are prohibitive.
Conventional heterostructures have already attained improved performance for high frequency group III-V semiconductor devices such as GaN devices. Initially, gallium arsenide (GaAs) metal-semiconductor field effect transistors (MESFETs) were the dominant devices for high frequency applications. Subsequently, several different heterostructures were developed in this material system, including AlGaAs/GaAs, (ΔEg ˜0.4 eV) and InAlAs/InGaAs (ΔEg ˜0.8 eV). High electron mobility transistors (HEMTs) utilizing these heterostructures can outperform their MESFET counterparts. For example, the optimized MESFETs show a maximum operating frequency (fmax) of 160 GHz, while GaAs pseudomorphic high electron mobility transistors (PHEMTs) have attained maximum frequency (fmax) values of 290 GHz, and InP PHEMTs have attained frequencies of 600 GHz.
Currently, GaN films are produced by hetereoepitaxial growth on either single crystal SiC or sapphire. Due to the lattice mismatch between GaN (4.8 Å) and sapphire (4.763 Å) or 4H-silicon carbide (3.0730 Å), a significant number of threading dislocations are formed during the growth process.
In the search to achieve large diameter, low defect, high quality SiC structures at affordable prices, SiC has become an important wide bandgap group III-V semiconductor because of its excellent properties for high power microwave devices. SiC thus competes with GaAs and Si in terms of gain, power output and efficiency at X-band, and promises even better performance at higher frequencies (Ka and Ku-bands). A particular goal for this technology is efficient broadband power RF transmitters that have high efficiency and high linearity, as well as rugged and low noise receivers for transmit/receive (T/R) modules for microwave applications.
As the technology advances, silicon carbide has become a good candidate. However, no heterostructure device has been achieved due to the unavailability of suitable SiC heterostructure material.
There is thus a need for practical metal-doped SiC materials that fulfill the requirements for wide bandgap semiconductor devices.